Sea turtles are faithful—to their nesting beaches, that is. Females of all seven sea turtle species return to the same beach time and again to nest, coming ashore at night to lay their eggs before returning to the ocean.

But scientists have found the mood lighting has to be just right. Bright lights from beachfront development can deter a female from returning to her nesting site, limiting the number of eggs laid each year. Those same lights disorient hatchlings, which can end up scrambling toward a porch light instead of following the moon’s reflection on the water toward the sea.

Now research inspired by one teenager’s high school project shows how dimming those lights has dramatically benefited Florida’s sea turtles.

“It’s a success story,” said University of Central Florida biology professor John Weishampel, coauthor of a new study published in the journal Remote Sensing in Ecology and Conservation. “Florida’s coastlines are getting darker, and that’s a good thing, not just for sea turtles but for other organisms.”

Image A shows average nighttime light levels in Florida from 1992 to 2012. Image B shows decreasing light levels over time, denoted by a lower slope value, in many nesting areas. (Photos: Courtesy University of Central Florida)

Weishampel said the study began a year ago, after his son, Zachary, had completed a remote sensing project in high school that investigated water quality in Florida’s lakes.

“While on a turtle walk with some friends from out of town, I noticed the light coming from a nearby city,” Zachary, 16, wrote in an email. “Growing up with an environmental science professor as my father, I already knew some of the effects of light pollution on the natural world.”

He was soon digging in to examine satellite imagery of artificial-light intensity along state beaches.

“I had seen a recent paper from a study in Israel that used satellites to relate to turtle nesting,” Weishampel said. “Knowing that Florida has many more nesting females and that the data go back nearly 30 years, I suggested that [Zachary] do the comparison.”

The two took the artificial-light-intensity data taken from 1992 to 2012 by the Defense Meteorological Satellite Program and overlapped it with annual records of nesting sea turtle sites from the Florida Fish and Wildlife Conservation Commission over the same period.

They found that nighttime light intensity levels lessened in more than two-thirds of the 368 beach locations they studied, despite the state adding 5.5 million people over the past two decades.

The main reason? Light rules. Local governments started cracking down on beachfront light pollution in the early 1990s, enforcing cutoff times for certain light sources, installing downward-directed light poles, and changing bulbs to emit longer-wavelength light that doesn’t disturb turtles as much.

Lower levels of light pollution, along with other conservation efforts, have led to success stories such as the green sea turtle recovery at Florida’s Archie Carr National Wildlife Refuge, where a record 14,152 nests were counted last fall, up from 6,023 nests in 2011.

The improved health of Florida’s subpopulation has led federal wildlife officials to propose that green sea turtles’ status under the Endangered Species Act be downgraded from endangered to threatened.

“Sea turtle populations are doing pretty well in Florida, and it may be due in part to our coastal management,” Weishampel said. “It shows we affect turtles’ nesting, but at the same time, we’ve been successful at reducing that effect. The satellite serves as a kind of policeman in the sky to see what’s going on with these lighting ordinances.”

With one published study under his belt, Zachary said that while he enjoys environmental science, he’s planning for a career in the medical field, perhaps sports medicine.

As for working with his father: “Eh, it had its ups and downs,” Zachary said.

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